    {:comment "c00"
     :schema-symbol 'c00 ;; used by over-each-parent to know where to put children.
     :first :comp
-    :comp {:synsem {:subcat '()}}
-    :head {:synsem {:subcat '()}}}))
+    :comp {:synsem {:subcat []}}
+    :head {:synsem {:subcat []}}}))
 
 (defonce h00
   (unify-check

  (merge
   (unify
    h21
    {:head {:synsem {:subcat {:2 {:subcat {:2 '()}}}}}})
   {:comment "h21a"
    :schema-symbol 'h21a}))


                                modified
                                (let [sem (atom :top)
                                      essere (atom :top)]  ;; TODO: use (default) to set this for all {:cat :verb} rules.
                                  {:synsem {:subcat []
                                            :cat :verb
                                            :essere essere 
                                            :sem sem}
                                   :comp {:synsem {:cat :prep
                                                   :subcat []}}
                                   :head {:modified false
                                          :synsem {:cat :verb
                                                   :essere essere
                                                   :sem sem
                                                   :subcat []}}
                                   :rule "s-modified-modifier-last"}))))

(defn aux-is-head-feature [phrase]
